In many fields, it is important to detect or quantify an oxidant and a substance that generates an oxidant as a result of a chemical reaction. Particularly, in the water treatment field, it is very important to quantify and monitor an oxidant in water in order to manage a water treatment effect and operation of a water treatment apparatus.
Conventionally, for example, an enzymatic method or a method for measuring a substance that chemically reacts with an analyte to generate a detectable change (such as a color change) is proposed as a method for quantitative determination of oxidant, and used in quantitative determination of various components existing in a body fluid in a clinical inspection or an environmental analysis. For example, in the quantitative determination of hydrogen peroxide, under coexistence of peroxidase, a substance such as leuco dye in which the detectable color change is generated is added as a reducing agent to cause a redox reaction, and a quantitatively-produced coloring substance is subjected to a colorimetric analysis (for example, see Patent Document 1).